The present invention relates generally to medical devices. More particularly, the invention relates to methods and devices for selectively diverting blood flow to the cerebral vasculature from the aorta in patients having stroke or cardiac arrest. More particularly, the invention relates to apparatus and methods which provide an aortic shunt and a venous return cannula for augmenting and/or cooling oxygenated blood to the brain. The devices and methods also provide mechanisms for variable blood flow through the aorta.
Patients experiencing cerebral ischemia often suffer from disabilities ranging from transient neurological deficit to irreversible damage (stroke) or death. Cerebral ischemia, i.e., reduction or cessation of blood flow to the central nervous system, can be characterized as either global or focal. Global cerebral ischemia refers to reduction of blood flow within the cerebral vasculature resulting from systemic circulatory failure caused by, e.g., shock, cardiac failure, or cardiac arrest. Within minutes of circulatory failure, tissues become ischemic, particularly in the heart and brain.
Cardiac arrest is defined as abrupt cessation of cardiac pump function, e.g., from myocardial infarction with loss of substantial muscle mass, acute myocarditis, or from depression of myocardial contractility following prolonged cardiopulmonary bypass. Mechanical abnormalities, such as severe valvular stenosis, massive aortic or mitral regurgitation, acutely acquired ventricular septal defects, can also cause cardiac arrest by reducing cardiac output. Additional causes of cardiac arrest include arrhythmia, such as ventricular fibrillation and ventricular tachycardia.
With sudden cessation of blood flow to the brain, complete loss of consciousness is a sine qua non in cardiac arrest. Cardiac arrest often progresses to death within minutes if active interventions, e.g., cardiopulmonary resuscitation (CPR), defibrillation, use of inotropic agents and vasoconstrictors such as dopamine, dobutamine, or epinephrine, are not undertaken promptly. The most common cause of death during hospitalization after resuscitated cardiac arrests are related to the severity of ischemic injury to the central nervous system, e.g., anoxic encephalopathy. The ability to resuscitate patients of cardiac arrest is related to the time from onset to institution of resuscitative efforts, the mechanism, and the clinical status of the patient prior to the arrest.
Focal cerebral ischemia refers to cessation or reduction of blood flow within the cerebral vasculature resulting from a partial or complete occlusion in the intracranial or extracranial cerebral arteries. Such occlusion typically results in stroke, a syndrome characterized by the acute onset of a neurological deficit that persists for at least 24 hours, reflecting focal involvement of the central nervous system and is the result of a disturbance of the cerebral circulation. Other causes of focal cerebral ischemia include vasospasm due to subarachnoid hemorrhage or iatrogenic intervention.
Traditionally, emergent management of acute ischemic stroke consists of mainly general supportive care, e.g. hydration, monitoring neurological status, blood pressure control, and/or anti-platelet or anti-coagulation therapy. Since 1996, tissue plasminogen activator (t-PA) or Activase(copyright) , was approved by the FDA for treatment of acute stroke. However, treatment with systemic t-PA is associated with increased risk of intracerebral hemorrhage and other hemorrhagic complications. Aside from the administration of thrombolytic agents and heparin, there are no therapeutic options currently on the market for patients suffering from occlusion focal cerebral ischemia. Vasospasm may be partially responsive to vasodilating agents. The newly developing field of neurovascular surgery, which involves placing minimally invasive devices within the carotid arteries to physically remove the offending lesion may provide a therapeutic option for these patients in the future, although this kind of manipulation may lead to vasospasm itself.
In both stroke and cardiac arrest, patients develop neurological deficits due to reduction in cerebral blood flow. Treatments should include measures to increase blood flow to the cerebral vasculature to maintain viability of neural tissue, thereby increasing the length of time available for interventional treatment and minimizing neurologic deficit while waiting for resolution of the ischemia.
New devices and methods are thus needed for augmentation of cerebral blood flow in treating patients with either stroke or cardiac arrest caused by reduced cerebral perfusion, thereby minimizing neurologic deficits.
The invention provides vascular constriction devices and methods for augmenting blood flow to a patient""s cerebral vasculature, including the carotid and vertebral arteries, while maintaining peripheral circulation. The devices constructed according to the present invention comprise an aortic shunt, having first and second tubular members. The first member has a first diameter suitable for passage through the aortic lumen and is expandable to a second diameter suitable for frictionally engaging the aortic lumen. In certain embodiments, the first member comprises a self-expanding stent, or an expandable cylindrical or toroidal balloon. The first member has a length which spans from the ascending aorta upstream of the brachiocephalic trunk to the descending aorta downstream of the left subclavian artery. The first member also includes a lumen that communicates with proximal and distal openings, and a side opening adapted to communicate with the carotid arteries.
The second tubular member is nested within the first tubular member. The second member includes a lumen communicating with proximal and distal openings. The distal opening is aligned with the side opening of the first tubular member. This structure allows blood flow through the ascending aorta through the first member into the descending aorta, and through the second tubular member into the carotid arteries.
In another embodiment, the distal end of the second tubular member communicates with a port or a plurality of ports mounted on an intermediate portion of the first tubular member. The port(s) are adapted to communicate with the carotid arteries. The proximal end of the second tubular member extends through an incision on a peripheral artery, e.g., femoral artery, outside of a patient""s body and is adapted to receive infusion of oxygenated blood or cooled solution, which passes through the lumen and port(s) of the second tubular member into the carotid arteries.
In another embodiment, a cooling coil is included in the second member for cooling blood passing through the second member before flowing into the carotid arteries. A thermometer is optionally mounted in the first member, second member, and/or the cooling coil for measuring temperature of blood flow upstream and downstream the device and into the carotid arteries. In certain embodiments, a pump and a mechanism are included in the second member to, respectively, facilitate and to provide variable blood flow from the aorta into the carotid arteries.
The present invention also provides venous return cannulas for receiving blood from the cerebral venous circulation. When used in conjunction with the aortic shunts described above, the venous return cannulas allow the cerebral circulation to be isolated from the systemic circulation in selective cooling of the cerebral circulation. This is particularly helpful in minimizing complications associated with systemic cooling, e.g., disseminated intravascular coagulation (DIC). The cannula has an elongate tubular member having a lumen communicating with a proximal end and a port at a distal end. The distal port is adapted to receive venous blood from the jugular veins. An inflatable chamber is included in the distal end, and when expanded, is adapted to engage the lumens of the right and left subclavian veins at a position where the jugular veins and the subclavian veins join the superior vena cava. The chamber also includes first and second ports that are adapted to receive blood from the right and left subclavian veins and pass the blood into the superior vena cava.
In using the aortic shunts described above for treating patient with stroke and/or cardiac arrest, the aortic shunt is first advanced into the aorta through an incision on a peripheral artery, e.g., the femoral artery. The shunt is positioned so that the proximal opening of the first tubular member is upstream of the brachiocephalic trunk, the distal opening of the first tubular member is downstream of the left subclavian artery, and the side opening communicates with the carotid arteries. The shunt is expanded so that the first tubular member engages the lumen of the aorta. Oxygenated blood flows from the ascending aorta through the first tubular member into the descending aorta and through the second tubular member into the carotid arteries. Blood is cooled when passed through the second member. Alternatively, cooled oxygenated blood or neuroprotective solution is infused through the proximal end of the second tubular member and passed through the ports mounted on an intermediate portion of the first tubular member. Blood flow to the brain can be varied by varying the diameter of the second tubular member, similar to a coarctation device, as described in Barbut, U.S. application Ser. No. 09/260,371, filed Mar. 1, 1999, incorporated herein by reference in its entirety.
In another method using the venous return cannula, the cannula is inserted through an incision on a peripheral vein, e.g., the right or left subclavian vein. The inflatable chamber is positioned at the junction of the right and left subclavian veins with the superior vena cava. The chamber is inflated so that the first and second ports on the chamber engages, respectively, the right and left subclavian veins. Venous blood flows from the right subclavian and left subclavian veins through the first and second ports and into the superior vena cava, whereas the hypothermic blood infused through the aortic shunt into the carotid arteries is passed from the jugular veins into the port(s) at the distal end of the cannula. Removed venous blood is then re-cooled and pumped back into the cerebral circulation via the aortic shunt. In this way, isolation of cerebral and systemic circulation is maintained.
It will be understood that there are many advantages in using the partial aortic occlusion devices and methods disclosed herein. For example, the devices can be used (1) to provide variable partitioning of blood flow between cerebral and systemic circulation; (2) to augment and maintain cerebral perfusion in patients suffering from global or focal ischemia; (3) to prolong the therapeutic window in global or focal ischemia; (4) to accommodate other medical devices, such as an atherectomy catheter; (5) to provide selective cooling to the cerebral vasculature; and (6) by an interventional radiologist, neuroradiologist, or cardiologist in an angiogram or fluoroscopy suite.